Fin Whale
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FIN WHALE Scientific name: Balaenoptera physalus |
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Distribution within the Mediterranean:
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Taxonomy: PHYLUM: Chordata |
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Conservation status in the Mediterranean: Vulnerable (IUCN) |
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Conservation status in the world: Endangered (IUCN) |
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Mean length:
Between 17 and 22 meters in adults |
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Habitat:
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Diet:
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Identification characteristics:
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Can be confused with:
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Blow and diving pattern:
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Individual identification characteristics:
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Main threats:
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The fin whale (Balaenoptera physalus) is the largest baleen whale found in the Mediterranean Sea. It is the world’s second largest cetacean, after the blue whale (Balaenoptera musculus).
The Fin whale has a long body that is slender and streamlined with a rather small and falcate dorsal fin, located at the beginning of the last third of the animal’s body. It rises at a shallow angle from the animal’s back. The flippers are short and slender, with a pointy edge, dark on the dorsal side and pale on the ventral. The coloration pattern is characteristic of the species. The body is black or dark grey on the dorsal part and the sides and light on the ventral part. There also are some whitish V-shaped chevrons (pointing forward) on the dorsal part of the head, just behind the blowholes and some light streaks coming up from the belly, especially from the area near the flippers. The most unique characteristic is that there is an asymmetric pattern in the coloration of following structures:
- The left lower jaw is mostly dark while the right lower jaw is mostly white.
- There is a light patch extending up and back on the right side of the head.
- V-shaped chevron starting between the two blowholes and pointing forward, but extending backwards. The right side is lighter.
These asymmetrical marks are characteristic of every individual, and therefore can be used as unique marks for each individual in photo identification studies.
Fin whales have between 260 and 480 baleen plates on each side. Their colour is dark grey almost black, except for the ones on the front-right side, which are white. They have between 50 and 100 throat pleats, which allow them to expand their mouth cavity while feeding.
The body size of the Mediterranean fin whale subpopulation is similar to the size of the individuals that live in the Atlantic, and a little bit longer than the ones that inhabit the continental shelf in front of the NE of the United States. The maximum length is 22,5 meters for females and 21 meters for males, although the average length is 15-19 meters. The maximum weight ever recorded is 90.000 kg. In the Mediterranean, the length of newborns is about 5,2 meters for males and females, a bit smaller than the ones in the Pacific, which measure between 6 and 6,5 meters.
DISTRIBUTION AND MIGRATORY PATTERNS WITHIN THE MEDITERRANEAN SEA
The fin whale is the most common baleen whale species in the Mediterranean Sea, but it has not been reported in the Black Sea. There are thought to be 5.000 individuals in the Mediterranean subpopulation. Its distribution is not regular along the basin, but there are certain areas where its abundance is higher. One of these zones is the region located between the Gulf of Lion, the northwest coast of Corsica, the north and west coasts of Sardinia and the coast of Liguria, which is the region with the highest abundance of fin whales. The Ligurian sea, declared as a Marine Protected Area on 1999 with the name of Pelagos Sanctuary for Mediterranean Marine Mammals, is located in this region. The fin whale is also common in the areas between Corsica, Sardinia, Sicily and the western Italian coast, and the region west of Corsica and Sardinia. The eastern parts of the Mediterranean basin have the lowest densities for this species.
It is well known that the fin whale distribution changes seasonally during the year. In this sense, the Ligurian Sea is their main feeding ground and consequently they tend to aggregate there in summer. The winter distribution of the species is less clear. It has always been thought that the individuals spread out to other regions of the Mediterranean, but this aspect is not as clear as previously thought. There are some individuals that spend the whole year in the Ligurian Sea, others that travel to the Alboran Sea, located between the northern coast of Africa and the southern coast of Spain. There are several fin whales that have migratory movements during spring and autumn. In fact, some acoustical studies have shown, that there are fin whales in the Catalan Sea during spring and autumn. It is not infrequent to see them travelling in areas close to the Cap de Creus.
There are also some individuals that feed in the Ligurian Sea during summer, which come from the NE Atlantic subpopulations. These are individuals that migrate every year from Atlantic waters to the Ligurian Sea and then go back to the Atlantic Ocean during winter.
HABITAT AND FEEDING
The fin whale is a pelagic animal, commonly seen in oceanic waters, although it can also be spotted on the continental shelf. The mean depth of the zones where this animal has been sighted in the Mediterranean sea vary between 1775 and 2300 meters, although it is also possible to see some individuals closer to the coast. This shows that the habitat of the fin whale can vary within the Mediterranean basin. In the rest of the world, the habitat of this species is characterized by having great densities of its main prey and by the physical and biological conditions that allow these accumulations. The distribution of the fin whale in the Mediterranean Sea is thought to suffer seasonal changes and to vary from one year to the next. This species tends to distribute in a heterogeneous way, concentrating in those regions with a higher prey density.
The fin whale is a generalist predator with a wide spectrum of possible prey, ranging from copepods or small crustacean like the euphausiids, to small fish like the capelin (Mallotus villosus), herring (Cuplea harengus), anchovy (Engraulis encrasicolus), sand lances (Ammodytes sp.) and most commonly the European pilchard (Sardinus pilchardus). The diet of the Mediterranean fin whale is much more specialized and they only feed on a specific kind of prey. Many different studies show that the only prey of the individuals that feed in the Ligurian Sea is the northern krill (Meganyctiphanes norvegica). A recent study shows that the prey of the fin whales that feed in the area surrounding the isle of Lampedusa is different kind of krill (Nictyphanes couchii). Other authors think that they could also feed from other species when the abundance of their main prey decreases.
The fin whale has a very specific feeding strategy adapted to its morphology, its physiology and to the prey distribution. It consists of swimming rapidly into a school of krill, and just before reaching it, slowing down and opening its mouth at the same time, using the throat pleats to reach its maximum mouth capacity. Big amounts of krill and water enter the mouth due to the negative pressure generated by the fin whales manoeuvre. When the whale closes its mouth, the water and the krill remain inside it. Next the animal applies a large amount pressure using its tongue and the ventral walls of its mouth, and the water exits the mouth through the baleen plates, but the prey, which is to big to pass through is trapped.
REPRODUCTION AND LIFE HISTORY
Although it has been noted that births of new individuals can occur throughout the year, they tend to concentrate in the months between September and January, especially in November. This wider reproduction period, compared to other population of the same species, may be a consequence of the environmental conditions of the Mediterranean sea. The Mediterranean fin whale doesn’t appear to have a specific breeding ground, as other baleen whale species have, but seem to be spread out all over the Mediterranean basin during their breeding season.
Its mating system is believed to be based on competition between males in order to copulate with a female. Gestation last for 11-12 months and they achieve sexual maturity by the age of 6-7 years for the males and by the age of 7-8 years for the females. They can live for 80 or 90 years.
ECOLOGY, BEHAVIOUR AND IDENTIFICATION
The fin whale is quite a fast swimmer that can reach speeds of 30 km/h. Its swimming pattern is quiet. It doesn’t normally show aerial displays, only when an individual feels threatened. When it breaches, it rises its body above the sea level, but for the caudal part, which remains under the water. During the fall, the fin whale may rotate its body. It produces a big splash and a loud noise when it crashes into the water. Dives aren’t normally very deep (between 100 and 200 meters) and they last for 3 to 10 minutes. In the Mediterranean, dives can be a little bit deeper, reaching the 470 meters. These deeper dives suggest that fin whales in the Mediterranean have developed different diving habits in order to adapt to the daily vertical migration of their prey.
The fin whale is not a gregarious animal and it normally moves in small groups. The only perceptible social bonds are the ones between mothers and their calves, but this usually disappears after weaning. The mean group size in the Mediterranean Sea ranges between 1,3 and 1,7 individuals per group and is smaller than in other regions.
Fin whale are capable of communication by emitting 20 Hz pulses that are used for long distance communication.
Due to the large size and the relatively fast speed of the fin whale, the only natural predator of the species is the killer whale (Orcinus orca).
It is relatively easy to distinguish the fin whale from other species in the Mediterranean Sea. Firstly, because it is the only baleen whale that has a stable population in the Mediterranean sea. Secondly, because there is only one other cetacean species big enough to be confused with the fin whale that is commonly seen in the Mediterranean Sea, the sperm whale (Physeter macrocephalus) and there are several characteristics that help in their differentiation. It is relatively easy to distinguish the fin whale in the sea thanks to its slender and tall blow (up to 4-6 meters high), and its diving and swimming sequence. On the surface they usually blow 2-5 times in 10-20 seconds intervals before preforming a deeper dive, which normally lasts for 5-15 minutes. The dorsal side of the head is the first part to come out of the water when the fin whale surfaces to breath. Depending on the depth of the previous dive, the surfacing angle changes, being smaller for shallower dives. After surfacing, the whale blows while the dorsal part of the animal comes out of the water. After a short period of surface swimming, during which the whole body gradually emerges in an anterior-posterior way, the dorsal fin appears. When the dorsal fin is about to disappear under the waterline, the tail stock begins to curve. The more pronounced the bending of the tail stock is, the deeper the next dive is going to be. Finally the fin whale completely disappears under the water. The fluke seldom surfaces during the entire sequence.
INDIVIDUAL IDENTIFICATION CHARACTERISTICS
Most cetacean species have characteristics that change between individuals and that can be used in order to differentiate the individuals in photo-identification studies. The fin whale has three traits that can be use to distinguish the different individuals: the coloration patterns, the dorsal fin and the marks and scars on its body.
Coloration patterns: All the individuals have typical marks or patches. Their variability amongst the individuals is high enough to show significant differences between them and to allow us to distinguish them apart. The most characteristic patterns are:
- Right mandible patch: White area on the lower right jaw.
- Blaze: Light area only found on the right side of the head, just above the jawline and anterior to the eye stripe. It widens and runs dorsally and laterally until an area close to the blowholes.
- Eye stripe: Dark line that originates at the eye and runs dorsally and backwards in an oblique way. It can be seen on both sides of the body.
- Ear stripe: Dark line originating from the eye and running dorsally and backwards in an oblique way. It can be seen on both sides of the body.
- Interlineal wash: Light area between the eye and the ear stripes.
- Chevron: Is a coloration v-shaped pattern originating just behind the blowholes and curving down both sides of the animal, first in a posterior way and afterwards in an anterior way.
Dorsal fin: As in many other cetacean species, the dorsal fin of the fin whale can be used in individual identification. In this case we focus on the shape of the fin and on the scars or notches, paying special attention to the posterior edge of the fin. The marks in this area tend to remain for longer on the body.
Marks or scars: Fin whales acquire marks and scars on their body surface during their life, due to their interaction with other individuals, predation, the jaws of lampreys and small sharks or as a consequence of a collision with a vessel (propeller marks). The position or the shape of the scars or marks (above all the ones on the dorsal part of the body), can be a good way to identify individuals and differentiate them from others.
CONSERVATION STATUS AND MAIN THREATS
The International Union for the Conservation of Nature (IUCN) listed the fin whale world under the status of threatened species. This species suffered a great exploitation by the whale industry during the last three generations (1929 – 2007). Because of this, the worldwide population of fin whales has declined by 70 %. Nowadays, fin whale catches have significantly decreased and it’s widely believed that the worldwide population of fin whales is increasing in number. The conservation status of the Mediterranean subpopulation is vulnerable, and it is believed that the population is decreasing. This species is listed on several conventions and agreements such as the Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the Appendices I and II of the Convention on Migratory Species and the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic Area (ACCOBAMS), which protects the fin whale from deliberate killing. In addition, the Ligurian Sea, which is the main feeding area of the fin whale in the Mediterranean Sea, was designated as a Marine Protected Area in 1999, also known as the Pelagos Marine Sanctuary for Mediterranean Marine mammals.
The major threats that fin whales have to confront in the Mediterranean Sea are mostly caused by human activities. The following threats are the ones that cause a higher mortality:
- Collisions with boats: The fin whale is the largest cetacean species most frequently involved in whale-ship strikes. In addition, the Mediterranean Sea is one of the marine regions with a higher level of maritime traffic, above all of big merchant vessels. The worst consequence of these collisions is the death of the animal, particularly when big vessels are involved. However the whale-ship strikes can also cause permanent marks and scars on the animal’s body (for example the ones caused by propellers), or even amputate important body structures such as the tail fluke.
- Environmental pollution: Marine mammals are located at the top of the food web. Therefore they are the most distinguished exponents of bioaccumulation in the marine environment. This process refers to the accumulation of chemical substances, mostly pollutants, in the animal’s tissues and organs, reaching a higher concentration than in the environment. Cetaceans tend to accumulate these substances in their blubber. Females give part of these pollutants to their calves during pregnancy and milking period. The most common pollutants are organochlorines such as DDT or PCBs, which could potentially affect the reproduction and the immune system of the fin whale.
- Noise pollution: Maritime traffic is the main producer of marine noise, which can affect cetaceans and create long-term impacts on their populations. It has been seen that whales change their behaviour as a consequence of noisy activities such as underwater drilling, military exercises, industrial activities and the navigation of nearby boats. In this regard, whales tend to increase their speed and the duration of their dives and they indefinitely interrupt some important behaviours such as feeding. The long-term effects of noise pollution are still unknown.
- Other threat factors include entanglement with different kinds of fishing gear, predation, diseases and parasites.
REFERENCES
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BENTALEB, T., MARTIN, C., VRAC, M., MATE, B., MAYZAUD, P., SIRET, D., DE STEPHANIS, R. & GUINET, C. 2011. Foraging ecology of Mediterranean fin whales in a changing environment elucidated by satellite tracking and baleen plate stable isotopes. Marine Ecology Progress Series. 438:285-302
CANESE, S., CARDINALI, A., FORTUNA, C. M., GIUSTI, M., LAURIANO, G., SALVATI, E. & GRECO, S. 2006. The first identified winter feeding ground of fin whales (Balaenoptera physalus) in the Mediterranean sea. Journal of the Marine Biological Association of the United Kingdom 86:903-907
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http://www.iucnredlist.org/details/2478/0
http://www.iucnredlist.org/details/16208224/0
http://www.cms.int/documents/index.htm
http://www.cites.org/esp/app/index.php
http://www.accobams.org/index.php?option=com_content&view=article&id=73&Itemid=63
